Oxidized β-1,4-oligoglucuronic acid, and preparation method therefor and uses thereof

ABSTRACT

An oxidized β-1,4-oligoglucuronic acid, and a preparation method therefor and uses thereof. By using abundant cellulose in the natural world as the raw material, all 6-site hydroxyl groups of the cellulose β-1,4-polyglucose is oxidized into carboxyl groups to form glucuronic acid under the action of a sodium bromide (NaBr)-2,2,6,6-tetramethyl piperidine oxide (TEMPO)-sodium hypochlorite (NaClO) oxidation system, and the oxidized oligoglucuronic acid having an open ring at an end is prepared by controlling reaction conditions. The compound has obvious anti-cerebral ischemia activity, and can be developed into a potential anti-cerebral ischemia drug.

TECHNICAL FIELD

The present invention belongs to the technical field of pharmaceutical compounds, and in particular, relates to an oxidized β-1,4-oligoglucuronic acid and preparation methods as well as uses thereof.

BACKGROUND

Cellulose is a class of straight-chain dextran with a polymerization-degree from 3000 to 5000 connected by β1→4 glycosidic bonds, the molecular structure of which is linear. Cellulose has certain strength and rigidity and is not easily to be hydrolyzed by a diluted acid or base, and is a main component of plant cell wall. Since humans and carnivores rarely contain β-glucosidase, cellulose can not be digested. Microcrystalline cellulose (MCC) is a purified, partially depolymerized cellulose, the main component of which is a linear polysaccharide bound by β-1,4-glucosidic bonds. It is white, odorless, and odorless and a crystalline powder composed of porous particles, thereby improving efficiency of using cellulose and is widely used in the fields of pharmacy, cosmetics, food, light chemical industry due to special properties, such as lower polymerization degree and larger specific surface area.

Glucuronic acid is a common carbohydrate molecule which, in body acts as part of the composition of glycosaminoglycan, such as heparan sulfate, chondroitin sulfate, and the like; and also appears in glycosyl moiety of small molecule glycosides. However, there is no poly-glucuronic acid or oligo-glucuronic acid in nature.

In recent years, the incidence and mortality of cerebrovascular diseases increase with the improvement of living standards and the aging of population, which have become one of the leading causes of death. Among them, ischemic cerebrovascular disease is a major part of cerebrovascular diseases. At present, drugs that have good therapeutic effects on cerebral ischemic diseases include traditional Chinese medicine compositions, traditional Chinese medicines, and the like, however the clinical efficacy of these drugs remains to be confirmed yet.

Therefore, it is of great significance to study new anti-cerebral ischemia drugs.

SUMMARY OF THE INVENTION

In view of the defects in the prior art as said above, an oxidized β-1,4-oligoglucuronic acid and preparation methods as well as uses thereof are provided. In the method of the invention, cellulose abundant in nature is used to oxidize hydroxyl to glucuronic acid by the action of sodium bromide (NaBr)-2,2,6,6-tetramethylpiperidine oxide (TEMPO)-hypochlorite (NaClO) oxidation system, and at the same time, oxidized oligoglucuronic acid with end-opened ring is prepared by controlling the reaction conditions. The inventors have shown that this compound has significantly increased the rate of proliferation of oxygen- and glucose-deprived hippocampal cells at a concentration of 1 μM in a dose-dependent manner. This type of compound exhibits significant anti-cerebral ischemia activity and can be developed into potential anti-cerebral ischemia drugs.

The object of the present invention is achieved by following technical solutions:

In one aspect of the present invention, an oxidized β-1,4-oligoglucuronic acid with a structure of general formula I and degree of polymerization of 1 to 20 is provided:

wherein n=0-19; and m=0, 1 or 2.

In another aspect of the present invention, a mixture of the above-mentioned oxidized β-1,4-oligoglucuronic acids consisting of oxidized α-1,4-oligoglucuronic acids having structure of general formula I′ is provided:

wherein n′ and m′ are average values of n and m for each oligo-glucuronic acid in the mixture, respectively, n′ is selected from 1.0 to 19.0; and m′ is selected from 0 to 2.0. n′ and m′ can be integers or non-integers, which are arithmetic means of n and m for each oligo-glucuronic acid in the mixture on a molar basis.

A further aspect of the invention relates to a process for preparing oxidized β-1,4-oligoglucuronic acid or mixtures thereof, comprising steps of:

(1) weighing microcrystalline cellulose (MCC) powder and mercerizing it to obtain mercerized MCC solution with a concentration of 10-20 mg/ml;

(2) sequentially adding 2,2,6,6-tetramethylpiperidine oxide (TEMPO) and sodium bromide to the mercerized MCC solution prepared in step (1), adjusting pH to 10˜11 with an alkaline pH adjuster, then adding a sodium hypochlorite solution and reacting for 5-10 hours at 40-80° C., and finally adding an organic solvent to quench the reaction;

(3) obtaining a mixture of oxidized β-1,4-oligoglucuronic acids through dialysis in a 500 Da dialysis bag, concentration and lyophilization, or optionally obtaining individual oxidized β-1,4-oligoglucuronic acid through chromatographic separation.

The present invention also relates to a composition, comprising the oxidized β-1,4-oligoglucuronic acids of general formula I according to the present invention or a mixture thereof and a pharmaceutically acceptable excipient or carrier.

In another aspect of the present invention, the use of the oxidized β-1,4-oligoglucuronic acid according to the present invention or a mixture thereof in the preparation of anti-cerebral ischemia drugs or brain nerve-protecting drugs is also provided. They can be used to treat or prevent ischemic damage to neurons caused by stroke, myocardial infarction, brain shock, neonatal asphyxia and traumatic brain injury.

In another aspect of the invention, a method is also provided for treating or preventing neuronal ischemic damage in a subject or protecting brain nerves of a subject, comprising administering to the subject an effective amount of the oxidized β-1,4-oligoglucuronic acid of general formula I or a mixture thereof.

In the present invention, oxidized β-1,4-oligoglucuronic acids of general formula I or a mixture thereof as an agent for treating or preventing neuronal ischemic damage or as an agent for protecting brain nerves is also provided.

In the above solutions, the neuronal ischemic damage is caused by stroke, myocardial infarction, brain shock, neonatal asphyxia and traumatic brain injury.

Outstanding effects of the present invention include: cellulose abundant in nature is used as a raw material for preparing oxidized β-1,4-oligoglucuronic acid, the preparation method is simple, conditions are mild, the cost is low, and it is readily to be industrialized. And this class of compounds exhibits significant anti-cerebral ischemia activity, has significantly increased the rate of proliferation of oxygen- and glucose-deprived hippocampal cells at a concentration of 1 μM in a dose-dependent manner, and can be developed into potential anti-cerebral ischemia drugs, such as ischemic damage to neurons caused by stroke, myocardial infarction, brain shock, neonatal asphyxia and traumatic brain injury.

For readily understanding and grasping the technical solutions of the present invention, specific embodiments of the present invention will be further described below with reference to the accompanying drawings of the embodiments.

DESCRIPTION OF DRAWINGS

FIG. 1 is a total ion chromatography (TIC) and a UV chromatogram at 210 nm of oxidized β-1,4-oligoglucuronic acid of Example 5;

FIG. 2 is a mass spectrum of peak 0 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid undec- and deca-saccharide;

FIG. 3 is a mass spectrum of peak 1 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid nonus-saccharide;

FIG. 4 is a mass spectrum of peak 2 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid oct-saccharide;

FIG. 5 is a mass spectrum of peak 3 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid hept-saccharide;

FIG. 6 is a mass spectrum of peak 4 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid hexa-saccharide;

FIG. 7 is a mass spectrum of peak 5 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid penta-saccharide;

FIG. 8 is a mass spectrum of peak 6 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid tetra-saccharide;

FIG. 9 is a mass spectrum of peak 7 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid tri-saccharide;

FIG. 10 is a mass spectrum of peak 8 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid bi-saccharide;

FIG. 11 is a mass spectrum of peak Speak 9 in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid mono-saccharide;

FIG. 12 is a mass spectrum of duodec-saccharide to vige-saccharide in Example 5, i.e., a mass spectrum of oxidized β-1,4-oligoglucuronic acid (dp12-dp20);

FIG. 13 is a ¹H-NMR spectrum of the oxidized β-1,4-oligoglucuronic acid in Example 6;

FIG. 14 is a ¹C-NMR spectrum of the oxidized β-1,4-oligoglucuronic acid in Example 6;

FIG. 15 shows effects of oxidized β-1,4-oligoglucuronic acid in Example 7 on hippocampal cells of normal mice;

FIG. 16 shows effect of oxidized β-1,4-oligoglucuronic acid in Example 7 on hippocampal cells of glucose and oxygen deprivation mice.

MODE FOR CARRYING OUT THE INVENTION

The method of the present invention will be described below by way of specific examples, but the present invention is not limited thereto.

In one aspect of the present invention, an oxidized β-1,4-oligoglucuronic acid with a structure of general formula I and degree of polymerization of 1 to 20 is provided:

wherein n is selected from 0-19; and m is selected from 0, 1 or 2.

When m=0, the terminal glucose molecule is oxidized to remove two —CH(OH)— units, when m=1, the terminal glucose molecule is oxidized to remove one —CH(OH)— unit, and when m=2, —CH(OH)— is not removed from the terminal glucose molecule, and only oxidation of hydroxyl occurs. In an oxidized β-1,4-oligoglucuronic acid, i.e., oxidized β-1,4-oligoglucuronic acid in which n is a certain number, products wherein m is 0, 1, and 2 can be present in a mixture, or can be individually present. Oxidized β-1,4-oligoglucuronic acids with different m values will possess similar biological activities.

In a preferred embodiment of the present invention, n is 1 to 9, which corresponds to disaccharide to decaccharide of the oxidized β-1,4-oligoglucuronic acid, each of which is separated and characterized in the present invention. More specifically, in the oxidized β-1,4-oligoglucuronic acid of formula I, when n is 0, it corresponds to oxidized mono-saccharide; when n is 1, it corresponds to oxidized disaccharide; when n is 2, it corresponds to oxidized trisaccharide, when n is 3, it corresponds to oxidized tetrasaccharide, when n is 4, it corresponds to oxidized pentasaccharide, when n is 5, it corresponds to oxidized hexasaccharide, when n is 6, it corresponds to oxidized heptasaccharide, when n is 7, it corresponds to oxidized oct-saccharide, when n is 8, it corresponds to oxidized nonus-saccharide, when n is 9, it corresponds to oxidized decasaccharide; and when n is 10, it corresponds to oxidized undec-saccharide. These oxidized oligosaccharides may be used in a form of one or more mixtures.

The oxidized β-1,4-oligoglucuronic acid of the present invention is characterized by an oligo-uronic acid structure of different carbon atoms with end-opened ring. In one embodiment, oligo-glucuronic acids with different numbers of carbon atoms at reducing ends may be present as a mixture and the oligo-uronic acid of different polymerization degrees may also be present as a mixture.

Another aspect of the invention relates to a mixture of oxidized β-1,4-oligoglucuronic acids with a structure of general formula I′

wherein n′ and m′ are average values of n and m for each oligoglucuronic acid in a mixture, respectively, n′ is selected from 0 to 19.0; m′ is selected from 0 to 2.0. Preferably, n′ is selected from 0 to 10.0 and m′ is selected from 0.5 to 1.8; and more preferably n′ is selected from 0 to 10.0 and m′ is selected from 0.8 to 1.5.

In another preferred embodiment, the oxidized β-1,4-oligoglucuronic acid mixture of the invention comprises more than 80%, preferably more than 90%, more preferably more than 95% of mono- to undec-mer of β-1,4-glucuronic acid (n is 0-9) with end-opened ring, where m′ is 0.8-1.5.

The oxidation process of the present invention comprises steps of mercerizing cellulose, oxidizing the cellulose solution, and post-treating oxidized products to form oxidized β-1,4-oligoglucuronic acid.

1. Mercerization of Cellulose

To prepare the oxidized β-1,4-oligoglucuronic acid of the present invention, the raw material, microcrystalline cellulose is mercerized to form a solution. The concentration of the solution is about 10 to 20 mg/mL. The applicant found that if the concentration of the solution is too high, it is not easy to completely perform the oxidation process, and if the concentration of the solution is too low, it will result in unhomogeneous oxidized products.

2. Oxidation of Cellulose Solution

The following oxidation system was used in the present invention: sodium bromide (NaBr)-2,2,6,6-tetramethylpiperidine oxide (TEMPO)-sodium hypochlorite (NaClO) oxidation system. Oxidation performance of the oxidation system is particularly suitable for obtaining the β-1,4-oligoglucuronic acid of the present invention by adjusting reaction conditions. Compared with conventional oxidants, the oxidation system of the present invention enables the oxidation reaction to proceed more completely so as to obtain a reaction product with end-opened ring without impairing the uniformity of the reaction system. In addition, proportions of substances in the oxidation system on a molar basis may be, for example, TEMPO:NaBr=1:5 to 1:50; glucose units in cellulose: active NaClO=1:0.5 to 1:5; TEMPO: Glucose unit in cellulose=1:1 to 1:5. In one embodiment of the present invention, the weight percentage of active sodium hypochlorite in the sodium hypochlorite solution is 1 to 20%, preferably 2 to 15%, more preferably 3 to 12%.

The oxidation reaction is carried out under alkaline conditions. Upon research, it was found that the optimum pH range is 10-11. When the pH value of the reaction system is too high, the oxidation efficiency is low. If the pH value is too low, it is not conducive to the oxidation. The pH value of the reaction is controlled by a basic compound, and the most preferred basic compound is NaOH solution. There is no particular restriction on NaOH solution.

The oxidation temperature of an oxidation reaction suitably used in the present invention is 40 to 80° C., preferably 50 to 70° C., more preferably 52 to 68° C. Oxidation within this temperature range will facilitate the removal of undesired residual enzyme, while obtaining uronic acid with end-opened ring. Without being bound to any theory, the inventors have found that a reaction temperature below 40° C. will be unfavourable for obtaining oxidized β-1,4-oligoglucuronic acid with end-opened ring. And if the reaction temperature is too high, biological activities of raw materials will be destroyed, thereby unfavourable for using reaction products.

After adding an organic solution to quench the reaction, the product solution obtained by oxidation is purified to obtain oxidized β-1,4-oligoglucuronic acid. As a preferred purification method, the obtained oligoglucuronic acid can be purified by dialysis, and in particular, the material used for dialysis should entrap a substance with a molecular weight of 500 Da, thereby purifying the oligosaccharide of the present invention. Other purification methods known in the art can also be used, as long as the purity of the oligoglucuronic acid obtained by dialysis can be ensured to be higher than 99%, more preferably higher than 99.5%.

The present invention also relates to the use of oxidized β-1,4-oligoglucuronic acid or a mixture thereof as an active compound component for preparing anti-cerebral ischemia drugs.

Cerebrovascular disease is the leading cause of death among middle-aged and elderly people in our country, and is also one of the focuses of the study of world health strategy. Among cerebrovascular diseases, the incidence of ischemic diseases ranks the first. In the case of mild ischemia/hypoxia, generally the brain compensatory mechanism protects central nervous system from injury. However, when the degree of ischemia is increased, irreversible nerve damages will occur, leading to a series of clinical symptoms and even death. Clinically, cerebrovascular accidents (such as stroke), myocardial infarction, shock, neonatal asphyxia and traumatic brain injury can cause ischemic damage to neurons. Therefore, it is of great significance to develop a natural source substance which can alleviate symptoms of cerebral ischemia and enhance the survival rate of brain cells.

The cell model used in the present invention for measuring symptoms of cerebral ischemia is a cell (OGD model) produced from HT-22 cells under oxygen and glucose deprivation conditions. HT-22 cells are a mouse hippocampal neuronal cell line that is a subclone of mouse T4 cell line and possesses characteristics of hippocampal neurons. Relevant contents can be found in, for example, Jeney Ramirez-Sanchez et al., Neurochemistry International 90 (2015) 215-223, “Neuroprotection by JM-20 against oxygen-glucose deprivation in rat hippocampal slices: Involvement of the Akt/GSK-Pathological”; Xiao-Jing Li et al., Journal of Ethnopharmacology 141 (2012) 927-933, Neuroprotective effects of Tong Luo Jiu Nao in neurons exposed to oxygen and glucose deprivation; TIAN-ZHI ZHAO et al., Neuroscience 328 126, “GPER1 Mediates Estrogen-Induced Neuroprotection Against Oxygen-Glucose Deprivation In The Primary Hippocampal Neurons”; and the like.

The present inventors found that the oxidized β-1,4-oligoglucuronic acid of general formula I or a mixture thereof can improve symptoms of cerebral ischemia and increase the survival rate of ischemic and hypoxia brain cells. Additionally, the oxidized β-1,4-oligoglucuronic acid of the present invention is derived from a natural product and is easily to be absorbed and utilized.

The present invention provides a pharmaceutical combination, comprising the oxidized β-1,4-oligoglucuronic acids as said above, and optionally a pharmaceutically acceptable excipient.

Methods for preparing various pharmaceutical combinations containing various proportions of active ingredients are known or will be apparent to a skilled person based on the disclosure of the present invention, which are, for example described in Remington's Pharmaceutical Sciences, Martin, E. W., ed., Mack Publishing Company, 19th ed. (1995). A method for preparing a pharmaceutical composition includes incorporation of a suitable pharmaceutical excipient, carrier, diluent and the like.

Pharmaceutical formulations of the present invention are manufactured by known methods, including conventional methods of mixing, dissolving or lyophilizing.

The pharmaceutical composition of the present invention can be administered to a patient in a variety of routes suitable for the selected administration mode, for example, orally or parenterally (by intravenous, intramuscular, topical or subcutaneous routes).

Therefore, the pharmaceutical combination of the present invention in combination with a pharmaceutically acceptable carrier (such as an inert diluent or an edible carrier) may be administered systemically, eg, orally. They can be enclosed in hard or soft shell gelatin capsules and can be compressed into tablets. For oral therapeutic administration, the active compounds of the present invention may be combined with one or more excipients and used in a form of swallowable tablet, buccal tablet, troche, capsule, elixir, suspension, syrup, disc and the like. Such composition and preparation should contain at least 0.1% of active compound. The proportions of such composition and preparation can of course vary and may range from about 1% to about 99% by weight of a given unit dosage form. In the therapeutically useful composition, the amount of active compound is such that an effective dosage level can be achieved.

Tablets, troches, pills, capsules and the like may also contain: binders such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; disintegrants such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, fructose, lactose or aspartame; or a flavoring such as peppermint, oil of wintergreen, or cherry. When the unit dosage form is a capsule, it may contain, in addition to the above type of material, a liquid carrier such as vegetable oil or polyethylene glycol. A variety of other materials may be present as a coating, or a physical form altering the solid unit dosage form by otherwise modes. For example, tablets, pills or capsules can be coated with gelatin, wax, shellac or sugar and the like. A syrup or elixir may contain the active compound, sucrose or fructose as a sweetening agent, methyl paraben or propyl paraben as a preservative, a dye and a flavoring such as cherry flavor or orange flavor. Of course, any material used to prepare any unit dosage form should be pharmaceutically acceptable and nontoxic in the employed amount. In addition, the active compounds can be incorporated into sustained release formulations and sustained release devices.

The active compounds can also be administered intravenously or intraperitoneally by infusion or injection. An aqueous solution of the active compound or salt thereof, optionally with a miscible non-toxic surfactant, may be prepared. Dispersants in glycerol, liquid polyethylene glycols, triacetin and mixtures thereof and oils may also be prepared. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

Pharmaceutical dosage forms suitable for injection or infusion may include a sterile aqueous solution or dispersions or sterile powder, where active ingredients in an instant preparation are contained in a suitable sterile injectable or infusible solution or dispersion agent (optionally encapsulated in liposomes). In all cases, the final dosage form must be sterile, liquid and stable under the conditions of manufacture and storage. Liquid carriers can be solvents or liquid dispersion media including, for example, water, ethanol, polyols (eg, glycerol, propylene glycol, liquid polyethylene glycols, etc.), vegetable oils, nontoxic glycerides, and suitable mixtures thereof. Proper fluidity can be maintained, for example, by forming liposomes, by maintaining the required particle size in the case of dispersions, or by using surfactants. Prevention of microorganisms can be brought about by various antibacterial and antifungal agents such as parabens, chlorobutanol, phenol, sorbic acid, thimerosal and the like. In many cases, it is preferable to include isotonic agents, such as sugars, buffers, or sodium chloride. Prolonged absorption of injectable compositions can be produced by using absorption-delayed compositions (eg, aluminum monostearate and gelatin).

Sterile injectable solutions are prepared by combining a required amount of active compounds in a suitable solvent with a required amount of various other ingredients enumerated above, followed by filtered sterilization. In the case of sterile powders for preparing sterile injectable solutions, the preferred method of preparation is vacuum drying and freeze-drying technique, which will produce a powder of the active ingredient with any otherwise required components present in a previously sterile-filtered solution.

Useful solid carriers include comminuted solids (such as talc, clay, microcrystalline cellulose, silica, alumina, etc.). Useful liquid carriers include water, ethanol or ethylene glycol or a water-ethanol/ethylene glycol mixture, in which an effective amount of the pharmaceutical combination of the present invention may optionally be dissolved or dispersed with the help of non-toxic surfactants. Adjuvants (such as flavouring agent) and additional anti-microbial agents can be added to optimize properties for a given use.

Thickeners (such as synthetic polymers, fatty acids, fatty acid salts and esters, fatty alcohols, modified celluloses or modified inorganic materials) may also be used in combination with liquid carriers for forming paintable pastes, gels, ointments, soap, etc., which can be directly applied on the user's skin.

The required therapeutic amount for a compound or a mixture thereof depends not only on the compound itself, but also on the administration mode, the nature of a disease to be treated, and the age and condition of a patient, and ultimately depends on the decision from an attending physician or clinician.

The above formulation may be presented in a unit dosage form, which is a physically discrete unit containing a unit dosage and suitable for administering to humans and other mammalian bodies. The unit dosage form can be a capsule or tablet, or many capsules or tablets. Depending on involved particular treatments, the unit dose of active ingredient may be varied or adjusted from about 0.1 to about 1000 mg or more.

The experimental methods described in the following examples are conventional methods unless otherwise specified. The reagents and materials are commercially available unless otherwise specified.

Example 1. Method for Preparing Oxidized β-1,4-Oligoglucuronic Acid

(1) 1 g of MCC powder was weighed, and mercerized with 50 ml of 10% NaOH solution to obtain a mercerized MCC solution;

(2) To the mercerized MCC solution prepared in step (1), 5 mg of TEMPO and 50 mg of sodium bromide were sequentially added, pH was adjusted to 10 with 5% NaOH solution, and 5 ml of sodium hypochlorite solution was added at a concentration of 5% weight on a basis of active hypochloric acid. At 55° C., the reaction was performed for 5 hours, and absolute ethanol was added to quench the reaction;

(3) Oxidized β-1,4-oligoglucuronic acid was obtained through dialysis in a 500 Da dialysis bag, concentration and lyophilization.

Example 2. Method for Preparing Oxidized β-1,4-Oligoglucuronic Acid

(1) 1 g of MCC powder was weighed, and mercerized with 50 ml of 10% NaOH solution to obtain a mercerized MCC solution;

(2) To the mercerized MCC solution prepared in step (1), 20 mg of TEMPO and 250 mg of sodium bromide were sequentially added, pH was adjusted to 10 with 10% NaOH solution, and 10 ml of sodium hypochlorite solution was added at a concentration of 5% weight on a basis of active hypochloric acid. At 40° C., the reaction was performed for 8 hours, and absolute ethanol was added to quench the reaction;

(3) Oxidized β-1,4-oligoglucuronic acid was obtained through dialysis in a 500 Da dialysis bag, concentration and lyophilization.

Example 3. Method for Preparing Oxidized β-1,4-Oligoglucuronic Acid

(1) 1 g of MCC powder was weighed, and mercerized with 100 ml of 10% NaOH solution to obtain a mercerized MCC solution;

(2) To the mercerized MCC solution prepared in step (1), 50 mg of TEMPO and 500 mg of sodium bromide were sequentially added, pH was adjusted to 11 with 30% NaOH solution, and 15 ml of sodium hypochlorite solution was added at a concentration of 5% weight on a basis of active hypochloric acid. At 70° C., the reaction was performed for 3 hours, and absolute ethanol was added to quench the reaction;

(3) Oxidized β-1,4-oligoglucuronic acid was obtained through dialysis in a 500 Da dialysis bag, concentration and lyophilization.

Example 4. Method for Preparing Oxidized β-1,4-Oligoglucuronic Acid

(1) 1 g of MCC powder was weighed, and mercerized with 100 ml of 10% NaOH solution to obtain a mercerized MCC solution;

(2) To the mercerized MCC prepared in step (1), 50 mg of TEMPO and 600 mg of sodium bromide were sequentially added, pH was adjusted to 11 with 50% NaOH solution, and 15 ml of sodium hypochlorite solution was added. At 60° C., the reaction was performed for 8 hours, and methanol was added to quench the reaction;

(3) Oxidized β-1,4-oligoglucuronic acid was obtained through dialysis in a 500 Da dialysis bag, concentration and lyophilization.

Example 5. Mass Spectrometry Test of Oxidized β-1,4-Oligoglucuronic Acid

5.1 Method

2 mg of oxidized β-1,4-oligoglucuronic acid obtained in Example 1 was weighed and dissolved in 1 ml of pure water. After filtration through a 0.22 μm microporous membrane, ultra-high performance liquid chromatography in series four Rod-time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) analysis was performed.

In UHPLC/Q-TOF-MS analysis, Agilent 6540 UHD Accurate-Mass Q-TOF LC/MS (Agilent Technologies, USA) system was used. Chromatographic conditions are listed as follows: ACQUITY UPLC BEH125 size exclusion chromatography column (4.6×300 mm, Waters); detection wavelength: 210 nm; mobile phase: A 50 mM ammonium acetate aqueous solution, B methanol, ratio 80% of A; flow rate 0.1 ml/min. Mass spectrometry conditions are listed as follows: negative ion mode; scanning range: 100-3000; temperature of dry gas: 350° C.; flow rate of dry gas: 8 L/min; capillary voltage: 3500 V; Fragment voltage: 80V.

5.2 Results

Upon UHPLC/Q-TOF-MS analysis of oxidized β-1,4-oligoglucuronic acid, following total ion chromatography (TIC) and UV chromatogram were obtained (see FIG. 1). As can be seen from FIG. 1, the peaks are distributed in a regular wave. Since molecular exclusion chromatography column was used, it is speculated that the wave peaks should be distributed from large to small according to polymerization degree. Structures were further speculated according to mass spectrum corresponding to each chromatographic peak (FIG. 2-11): FIG. 2 shows mass spectrum of peak 0, wherein there are three charges for m/z 655.7744, 645.7753 and 635.7728, and upon calculation, the molecular weights of the compounds represented by the three signals are 1970, 1940 and 1910 Da, respectively, and the corresponding structure are oxidized uronic acid oligosaccharides undec-saccharide, as shown in Formula I (n=10, m=0, 1 or 2). In addition, there are mass spectra signals with three charges, m/z 597.0981, 587.0991 and 577.0951, and mass spectra signals with two charges, 896.1517, 881.1502 and 866.1462, which are calculated to be three oxidized uronic acid oligosaccharides deca-saccharide with a molecular weight of 1794, 1764 and 1734 Da, respectively, corresponding to formula I (n=9, m=0, 1 or 2). Similarly, FIGS. 3 to 11 are mass spectra for peaks 1 to 9, which, upon structure analysis, are oxidized uronic acid oligosaccharides nonus-saccharide to mono-saccharide, as shown in formula I (n=8→0, m=0, 1 or 2). In chromatograms, duodec-saccharide to vige-saccharide are not well resolved, but there are relative clear signals in mass spectra, as shown in FIG. 12.

Example 6. Nuclear Magnetic Structure Confirmation of Oxidized β-1,4-Oligoglucuronic Acid

6.1 Methods

25 mg of sample obtained in Example 1 was accurately weighed, dissolved in 0.5 ml of heavy water (D≥99.96%) and analyzed by 600 MHz nuclear magnetic resonance spectrometer (Agilent, United States), wherein the concentration of internal standard trimethylsilylpropionate (TSP) was 0.2 μg/ml. Scanning time of hydrogen spectrum is 1 hour, and the test temperature is room temperature. Scanning time of carbon spectrum is more than 12 hour, and the test temperature is room temperature.

6.2 Results

NMR results are shown in FIG. 13 (¹H-NMR) and FIG. 14 (¹³C-NMR). It can be seen from hydrogen spectrum that a (4.70˜4.71 ppm) represents H at the first position of ring-closed glucuronic acid of β-configuration which is directly connected to or adjacent to ring-opened uronic acid, and region b (4.47˜4.60 ppm) represents H at the first position of ring-closed glucuronic acid of β-configuration which is far apart from ring-opened uronic acid and H at α-position of carboxyl when the reducing terminus of glucuronic acid is ring-opened and 2-CH₂O— are removed. It can be further seen from carbon spectrum that region 1 is peak of carboxy carbon, and region 2 is C at position 1 of uronic acid with closed-ring under different chemical environments. Combining hydrogen and carbon spectra analysis, it can be concluded that position 6 in structure unit of β-glucose was successfully oxidized to carboxyl, and the reducing terminus of glucuronic acid oligosaccharide was ring-opened with a certain degree of degradation, further demonstrating the results of mass spectrometry analysis.

Example 7. Effects of Oxidized β-1,4-Oligoglucuronic Acid on HT-22 Cells Under Oxygen and Glucose Deprivation (OGD) Conditions

7.1 Establishment and Experimental Grouping of OGD Model

Normally cultured HT-22 cells were taken, and the number of cells was adjusted to 2×10⁴ cells/ml. The cells were seeded in 96-well culture plates at 100 μl/well, and quadruplicate was set for each group (n=4). After pre-incubation for 12 hours, in administration group, 10 μl of samples of product obtained in Example 1 of different concentrations (1, 10, 100 μM) prepared in media were added respectively, and in the normal group, the same volume of media were added. The culture plates were incubated in 5% CO₂, 37° C. incubator for 12 h. Cell viability was observed and determined to determine the effects of the samples on normal cultured HT-22 cells.

The normal cultured HT-22 cells were taken, and the original culture medium was removed. The cells were washed twice with sugar-free DMEM medium and sugar-free DMEM medium was added to adjust the number of cells to 2×10⁴/ml. Cells were inoculated in 96-well culture plates at 100 μl/well. In administration group, 10 μl of samples of product obtained in Example 1 of different concentrations (1, 10, 100 μM) prepared in media were added respectively, and in the model group, the same volume of media were added. The culture plates were placed in an oxygen deprivation tank (inflated with 95% N₂, 5% CO₂) and incubated at 37° C. for 12 h. Cell viability was observed and determined to determine the effects of the samples on HT-22 cells under OGD.

7.2 Cell Viability Determined by MTT Assay

After the above groups of cells were cultured, 10 μL of MTT (5 mg/ml) solution was added to each well and cultured for another 4 hours. 100 μl of 10% SDS was added. After purple crystal was completely dissolved, OD values were measured at 570 nm and cell viability was calculated.

7.3 Results

Cell viability in each group was calculated by MTT method, as shown in Table 1, 2 and FIGS. 15, 16. As can be seen from Table 1 and FIG. 15, compared with normal group, there was no significant difference in cell viability after addition of low, medium and high doses of oxidized β-1,4-oligoglucuronic acid, indicating that oxidized β-1,4-oligoglucuronic acid is not toxic to HT-22 cells.

As can be seen from Table 2, compared with the control group, viability of HT-22 cells in the model group was significantly reduced (p<0.001), indicating that OGD significantly inhibited cell viability. However, after oxidized β-1,4-glucuronidic acid was added, cell viability was significantly higher than that of the model group (p<0.01) accompanied by a better dose-dependent relationship, indicating that oxidized β-1,4-oligoglucuronic acid possesses the effects of promoting the growth of HT-22 cells.

TABLE 1 Effects of oxidized β-1,4-oligoglucuronic acid on viability of normal HT-22 cells Concentration Viability Groups (μM) (%) Control group 100.00 ± 2.20  oxidized β-1,4-oligoglucuronic acid 1 97.39 ± 1.77 10 96.07 ± 0.96 100 94.78 ± 3.12 Data is expressed as mean ± SEM Compared with the control group: p < 0.05 significant difference (LSD test)

TABLE 2 Oxidized β-1,4-oligoglucuronic acid on viability of HT-22 cells under OGD Concentration Viability Groups (μM) (%) Control group 100.00 ± 2.09   Model group 62.98 ± 1.88^(### ) oxidized β-1,4-oligoglucuronic 1 81.13 ± 1.86**  acid 10 85.97 ± 3.92*** 100 93.44 ± 4.67*** Data is expressed as mean ± SEM ^(###)indicates p < 0.001 compared with the control group (LSD test) **indicates p < 0.01 compared with the model group (LSD test) ***indicates p < 0.001 compared with the model group (LSD test)

It can be seen from the above that oxidized β-1,4-oligoglucuronic acid or a mixture thereof of the present invention possesses a good anti-cerebral ischemia effect and similar results are also obtained in similar experiments using each isolated oxidized β-1,4-oligoglucuronic acid, which are useful in the preparation of anti-cerebral ischemia drugs.

There are various embodiments of the present invention, and all technical solutions formed by similar transformation or equivalent transformation shall fall within the protection scope of the present invention. 

The invention claimed is:
 1. An oxidized β-1,4-oligoglucuronic acid consisting of a structure of general formula I and polymerization-degree of 3 to 20:

wherein n is selected from 2-19; and m is selected from 0, 1 or
 2. 2. The oxidized β-1,4-oligoglucuronic acid of claim 1, wherein m=0.
 3. The oxidized β-1,4-oligoglucuronic acid of claim 1, wherein m=1.
 4. The oxidized β-1,4-oligoglucuronic acid of claim 1, wherein m=2.
 5. The oxidized β-1,4-oligoglucuronic acid of claim 1, wherein n=2-10.
 6. The oxidized β-1,4-oligoglucuronic acid of claim 1, wherein n is 2, 3, 4, 5, 6, 7, 8, 9 or
 10. 7. A mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula I′:

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0.
 8. The mixture of claim 7, wherein n′ is selected from 2 to 10.0 and m′ is selected from 0.5 to 1.8.
 9. The mixture of claim 7, wherein n′ is selected from 2 to 10.0 and m′ is selected from 0.8 to 1.5.
 10. The mixture of claim 7, wherein the components with n of 2-10 account for more than 80% by weight of the mixture.
 11. A preparation process for oxidized β-1,4-oligoglucuronic acid of claim 1, comprising following steps: (1) weighing microcrystalline cellulose powder followed by mercerizing to obtain mercerized microcrystalline cellulose solution with a concentration of 10-20 mg/ml; (2) sequentially adding 2,2,6,6-tetramethylpiperidine oxide (TEMPO) and sodium bromide to the mercerized microcrystalline cellulose solution prepared in step (1), adjusting pH to 10˜11 with an alkaline pH adjuster, then adding a sodium hypochlorite solution and reacting for 5-10 hours at 40-80° C., and finally adding an organic solvent to quench the reaction; (3) obtaining the oxidized β-1,4-oligoglucuronic acid of claim 1 through dialysis in a 500 Da dialysis bag, concentration and lyophilization.
 12. The preparation process of claim 11, wherein mass ratio of the microcrystalline cellulose powder to 2,2,6,6-tetramethylpiperidine oxide in step (2) is 1000:(5˜50).
 13. The preparation process of claim 11, wherein mass ratio of sodium bromide to 2,2,6,6-tetramethylpiperidine oxide in step (2) is ≤10:1.
 14. The preparation process of claim 11, wherein mass volume ratio of the microcrystalline cellulose powder to the sodium hypochlorite solution in step (2) is 1 g:(5˜15) ml.
 15. The preparation process of claim 11, wherein the organic solvent in step (2) is absolute ethanol or methanol.
 16. The preparation process of claim 11, wherein the alkaline pH adjuster in step (2) is 5˜50% (w/v) NaOH solution.
 17. A method of preparing an anti-cerebral ischemia medicament, comprising forming a medicament including the oxidized β-1,4-oligoglucuronic acid of claim 1 or a mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula I′:

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0.
 18. The method of claim 17, wherein the anti-cerebral ischemia medicament is used to treat ischemic damage to neurons caused by stroke, myocardial infarction, brain shock, neonatal asphyxia or traumatic brain injury.
 19. A method of preparing a brain nerve-protecting medicament, comprising forming a medicament including the oxidized β-1,4-oligoglucuronic acid of claim 1 or a mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula I′:

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0.
 20. A pharmaceutical composition, comprising the oxidized β-1,4-oligoglucuronic acid of general formula I of claim 1 or a mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula I′:

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0, and a pharmaceutically acceptable excipient or carrier.
 21. A method for treating ischemic damage to neurons of a subject, comprising administering to the subject in need thereof an effective amount of the oxidized β-1,4-oligoglucuronic acid of general formula I of claim 1 or a mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0.
 22. A method for treating ischemic damage to neurons of a subject, comprising administering to the subject in need thereof an effective amount of the oxidized β-1,4-oligoglucuronic acid of general formula I of claim 1 or a mixture of oxidized β-1,4-oligoglucuronic acid consisting of the structure of general formula I′:

wherein n′ and m′ are average values of n and m of claim 1 in the mixture, respectively, n′ is selected from 2 to 19.0; and m′ is selected from 0 to 2.0 wherein the ischemic damage to neurons is caused by stroke, myocardial infarction, brain shock, neonatal asphyxia or traumatic brain injury.
 23. The method of claim 21, wherein the ischemic damage to neurons is caused by stroke, myocardial infarction, brain shock, neonatal asphyxia or traumatic brain injury. 